1. Field of the Invention
The invention relates to a display device, and more particularly to a liquid crystal display (LCD) device with a bonding pad structure for electrically connecting external driving devices. An opening structure design on the bonding pad structure can provide an auxiliary electrical-connection path to replace a failed electrical-connection path caused by a defective conductive layer.
2. Description of the Related Art
Liquid crystal display (LCD) device is the most popular flat panel display and has characteristics of low power consumption, thin profile, light weight and low driving voltage. Generally, the LCD device has an array of pixel areas defined by scanning lines and data lines, and each pixel area has a pixel electrode and a thin film transistor (TFT) serving as a switching device. In addition, a plurality of bonding pad structures is fabricated on the terminals of the scanning lines and the data lines respectively to be electrically connected to external driving ICs through TAB (tape automatic bonding) or FPCB (flexible print circuit board) techniques, thus driving the pixel electrodes and providing image signals.
FIG. 1 is a plane view of a conventional LCD device. An LCD device 10 comprises a TFT substrate 12, a CF (color filter) substrate 14 and a liquid crystal material filling in a space between the substrates 12 and 14. A plurality of bonding pad structures is formed at the peripheral region of the TFT substrate 12 to be electrically connected to an external IC board 18 through a signal processing substrate 16, such as a TAB substrate or a FPCB.
FIG. 2 is a plane view of the TFT substrate 12 with bonding pads. The TFT substrate 12 comprises a plurality of scanning lines 20 and data lines 22 which vertically intersect to define an array of pixel areas 24. Each scanning line 20 has a terminal portion 20a, and a bonding pad 26 is formed overlying and electrically connected to the terminal portion 20a, thus the bonding pad 26 can be electrically connected to the external IC board 18 through the signal processing substrate 16. Similarly, each data line 22 has a terminal portion 22a, and a bonding pad 26 is formed overlying and electrically connected to the terminal portion 22a, thus the bonding pad 26 can be electrically connected to the external IC board 18 through the signal processing substrate 16.
FIG. 3 is a cross-section along line 3-3 of FIG. 2 to illustrate an example of a conventional bonding pad structure. On the peripheral region of the TFT substrate 12, a first metal layer M1 is patterned as the terminal portion 20a, a protection layer 25 is formed overlying the first metal layer M1 and has an opening to expose a predetermined electrical-connection area of the terminal portion 20a, and an ITO (indium tin oxide) layer is patterned as the bonding pad 26 to be electrically connected to the terminal portion 20a through the opening of the protection layer 25. Additionally, the first metal layer M1 is patterned as the scanning lines 20, and the ITO layer is patterned as pixel electrodes.
FIG. 4 is a cross-section along line 4-4 of FIG.2 to illustrate an example of a conventional bonding pad structure. On the peripheral region of the TFT substrate 12, a first metal layer M1 is patterned as the scanning line 20, a protection layer 25 is formed overlying the first metal layer M1, a second metal layer M2 is formed overlying the protection layer 25 and patterned as the terminal portion 22a, and an ITO (indium tin oxide) layer is patterned as a bonding pad 26 to be electrically connected to the terminal portion 22a. The second metal layer M2 is also patterned as the data lines 22, and the ITO layer is patterned as pixel electrodes.
FIG. 5 is a cross-section illustrating the conventional bonding pad structure of FIG. 4 electrically connected to the external IC board. In TAB or FPC processing, when defects are found and in need of repair, the TAB film or FPC film is stripped off, and then the glue of an anisotropic conductive film (ACF) 17 remaining on the glass is cleaned off, and then a new TAB film or FPC film is pasted on the glass substrate. The metal layers, however, may be scratched by improper operation during cleaning the remaining glue, subsequent testing steps or improper manual procedures. When the scratched portion 19 is large enough to crosscut the metal layer, the conductive particles of the ACF 17 adjacent to the scratched portion 19 encounter a problem of insufficient contact area. Thus, the electrical-connection path shown by an arrow dotted line fails to pass through the scratched portion 19, causing poor reliability and flawed product.